Variable displacement pump



April 18, 1961 R. J. PSCHUNDER VARIABLE DISPLACEMENT PUMP 5 Sheets-Sheet 1 Filed Sept. 18, 1959 a H HH IN VENTOR Ralph J .Psc'hunder BY 'fi ATTORNEYS April 18, 1961 R. J. PSCHUNDER VARIABLE DISPLACEMENT PUMP 3 Sheets-Sheet 2 Filed Sept. 18, 1959 IN VENTOR Ralph J. P5 chunder' ATTORNEYS 3 Sheets-Sheet 5 ATTORNEYS R. J. PSCHUNDER VARIABLE DISPLACEMENT PUMP R alph J .Ps chun der BY M 53,1

April 18, 1961 Filed Sept. 18, 1959 m w a w a m a OM. a 9 l w 8 6 3 Q A? 9 A? x 3 v M 5 M JD 7 7 Av A WKM 6 z 6 4 ws W 5 4 i AF W 4 .4 7 W A: 4% i A 4 n. 5 3 ,5 A%/ A. 5 W- !KJQ 5 N A. 3 2 2K 5M 1%,? 5W 5 5 W mud m5 k x m m O 5 6 M 7 m W 6 e w R; m m 1 1 F m F F F F Uniw stawsP w Q VARIABLE DISPLACEMENT PUMP" Ralph Pschunder, Moorestown, N.J., assignor to The JNew York Air Brake Company, a corporation of New ersey Filed Sept. 18, 1959, Ser. No. 840,958 18 Claims. c1. 103 -42 This invention relates to reciprocating piston pumps and more particularly to devices for varying the displacement of such pumps.

The primeobject of this invention is to provide a reciprocating piston pump in'which the basic parts of the displacement controlling mechanism are located within the pistons themselves. Since the weight of a pump is,

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ends of these bores, variable volume working chambers 19 and 19'. Extending between each pair of aligned cylinder bores 17 and 17 is a coaxial plunger bore in which is mounted a piston plunger 21. These'plungers 21 abut the inner ends of pump pistons 18 and 18'. Piston shoes 22 and 22 are mounted for universal 'movement on the outer ends of the pistons 18 and 18, respectively.

Extending through, but spaced radially from, an axial bore formed in cylinder block 16, is adrive shaft 23 containing an axial bore 24 and radial passages 25 and 25' which are aligned with the inlet passages 26 and 26, respectively, formed in cylinder block 16. The shaft 23 is journalled in bearings 27 and 27 located on opposite sides of cylinder block 16 and is provided with aconventional running seal 28 at its left end. Carriedv by in general, proportional to its 'volume, this invention affords an unusually light-weight pump because it may be incorporated without affecting materially the overallfdimensions of the pump.

Other objects are to provide a pump in which the dis? placement controlling mechanism unloads the pistons and establishes a small by-pass flow for cooling purposes after the elfective displacement has been reduced to zero.

The preferred embodiment of the invention will now be described in detail with reference to the accompanying drawings, in which:

Fig. 1.is an axial sectional view of an opposed piston pump incorporating the invention.

Fig. 2 is a sectional view taken on line 2-2 of Fig. 1; a portion of the cylinder block being broken away to show certain details. 1

Fig. 3 is an enlarged sectional view of a portion of one of the pump pistons. I V Fig. 4is a sectional view taken on line 4-4 of Fig. 3, showing the relationship between the circular. spill-back passages in the piston and the elongated spill-back passages in the valve plunger.

Figs. 5-10 are enlarged sectional views of one pump piston and cylinder bore, showing the relationships between the various ports and passages at different piston positions during maximum displacement operation.

Figs. 11-16 are enlarged views similar to Figs. 5-10, respectively, but showing the relationships between the ports and pasages during minimum displacement operation.

Fig. 17 is a graph showing the effective displacement versus discharge pressure curve for the preferred embodiment.

Fig. 18 is a sectional view similar to Fig. 2, showing a modification.

Fig. 19 is a sectional view taken on line 19-19 of Fig. 18.

Fig. 20 is a graph showing the effective displacement versus discharge pressure curve for the Fig. 18 embodiment.

Fig. 21 is a graph showing the pressure gradient in one of the control manifolds of the Fig. 18 embodiment.

Referring to Fig. 1, the pump comprises ahousing 11 formed with inlet and discharge ports 12 .and 13 which communicate, respectively, with the space 14 within the housing and the annular discharge manifold 15. A cylinder block 16, containing two circular series of aligned cylinder bores 17 and 17', is pressed into a bore formed in housing lland isolates themanifold 15 from the space 14. Pump pistons 18 and 18' reciprocate in the bores 17 and 17', respectively, and define, with'the-inner closed the drive shaft 23 are two swash plates '29 and 29'; the former being an integral part of the shaft and the latter being splined to it, as shown. The cam faces 31 and 31' of these swash plates lie in parallel planes and are in sliding engagement with the piston shoes 22 and 22'. The piston plungers 21 are of such length that the shoes carried by the two, sets of pump pistons are maintained inoperative engagement with the swash plates 29 and Coaxial with the two series of cylinder bores 17 and 17 are two similar series of bores 32 and 32 there being the same numberof bores in these series as in the series Each bore in series 32 is connected with one of the working chambers 19 by a passage 33 and a similar passage 33' connects each bore.32 with one of the working chambers 19. At their junction, each pair of aligned bores 32 and 32' is intersected by a passage 34 which communicates with the discharge manifold 15. Reciprocable in bores 32 and 32' are the check valves 35 and 35', respectively, which control communication, between passages'33 and 33' and the passage 34'. The check valves 35 and 35' carry stems which arereceived in bores formed in slotted stern guides 36 and 36' a which are held in place. by plugs 37 and 37' that close theouter ends of bores 32 and 32'. This arrangement of stems and guides affords hydraulic stops for the check valves. This type of check valve is more fully described and claimed in my copending application Serial No. 826,057,'filed July 9, 1959.

V Inasmuch asthe pistons 18 and 18 are identical, only one of the pistons 18 and its associated ports and passages will be described in detail. Each cylinder bore 17 is encircled by an annular port 38 that communicates with the inlet passage 26. Flow through this port into working chamber 19 is controlled by the edge 39 on the inner end of piston 18; the port 38 being open when the piston 18 is in its bottom dead-center position (Fig. 5) and being closed after the piston has completed about one-third of its discharge stroke (Fig. 7). Extending through each piston 18 is an axial bore 41 whose outer end is closed and sealed by plug 42 and whose inner end is fitted with a ported cap 43. The bore 41 is intersected by seven radial passages 44 which are of circular shape in cross-section and which open through the surface of piston 18. These passages are arranged to register with portj38 during that portion of the discharge stroke after edge 39 overtravels the port 38.

Reciprocable within axial bore 41 is a valve plunger 45 containing an axial bore 46 and six elongated radial slots 47 The plunger 45 is shiftable between limiting positions in which, respectively, it abuts the projection 48 of plug 42 and the cap 43 for disconnecting and connecting passages 44 and slots 47. The numbers and shapes of passages 44 and slots 47 ensure a substantial communicating fiow area when these parts are longitudinally aligned even though the plunger 45 and piston 18 are free to rotate relatively to each other. The plunger 45 is biased toward one limiting position by a coil compression spring 49 and is shifted in the opposite direction by the fluid pressure in control chamber 51 located between theouter iend'of the plunger and the plug 42.. Because of the fact that the valve plunger 45 is mounted within the piston 18, the spring 49 must be strong enough to hold the plunger in the Fig. 1 position against the acceleration forces which act on it, plunger 45, and the hydraulic oil in control chamber 51 as well as the suction forces which occur during the intake stroke. c v 1 Each piston 18 is also provided witha set 'of radial passages 52 which communicate with the control chamber 51 and are arranged to register with the port formed in the surface of cylinder bore 17 as the piston 18 approaches its bottom dead-center position. It should be noted that, as shown in Fig. 5, passages 52 are isolated from port 53 when the piston is in its bottom dead-center position. This arrangement forms an hydraulic stop for plunger 45 and minimizes the impact between itand projection 48. The port 53 is connected with an annular control manifold 54 which encircles cylinder block 16 and the pressure in this manifold, as well as control manifold 54, is controlled by a valve 55.

In the preferred embodiment, the displacement varying mechanism is employed as a discharge pressure compensator, i.e., it is designed to vary displacement in inverse relation to discharge pressure. As shown in Fig. 1, the valve 55 includes an inlet port 56 which is connected with the discharge manifold 15 by passage 57, a control port 58 which also communicates with passage 57, and two outlet ports 59 and 59" which are connected with the control manifolds 54 and 54', respectively, by passages 61 and 61'. Flow restrictions 62 and 63 are interposed between ports 56 and 58; respectively, and the passage 57. The control valve 55 is provided with a slidab'le plunger 64 which carries an edge 65 that graduates flow from inlet port 56 to the outlet ports 59' and 59. The plunger 64 is biased to the left to interrupt flow from the inlet to the outlet ports by a coil compression spring 66 and is shifted in the opposite direction by the fluid pressure in control port 53 which acts upon the shoulder 67. An axial bore 68, formed in plunger 64, interconnects the two outlet ports. Restricted passage 69, connecting passage 61 with the space 14 within the housing, serves to vent both control manifolds when the control valve 55 is in the Fig. 1 position.

The housing 11 also contains a by-pass port 71 which is connected by passages 72 and 72' with the annular grooves 73 and 73' that encircle cylinder block 16. Restricted passages 74 and 74' connect these grooves 73 and 73', respectively, with the cylinder bores 17 and 17'. The intersection of each passage 74 and bore 17 is so located that the passage 74 communicates with the passages 44 during a portion of each discharge stroke (see Fig. 8). When the passages 44 and slots 47 are in communication (i.e., during zero displacement operation), the passage 74, groove '73 and passage 72 create a small flow of fluid from cylinder bore 17 to port 71 which cools the pump.

During operation, fluid entering inlet port 12 passes into axial bore 24 formed in the drive shaft and is expelled by centrifugal action through passages 25 and 25' into inlet passages 26 and 26'. As each piston 18 moves on its suction stroke from the Fig. 7 position to the Fig. 6 position, the edge 39 uncovers port 38 thus permitting fluid in passage 26 to enter the working chamber 19. During the time required for the piston to' travel to its bottom dead-center position (Fig. 5) and back to the Fig. 6 position, the inlet passage 26 is open to the Working chamber 1 3'. When the piston again reaches the Fig. 7 position, this communication is interrupted. For the balance of the discharge stroke, the fluid displaced by piston 18 is forced through passage 33, check valve 35 and passage 34 to discharge manifold 15 and is discharged from the pump through port 13.

Y As long as discharge pressure is below the desired maximum, control valve plunger 64 remains in the Fig. 1 position and control manifolds 54 and 54 and ports 53 and 53' are vented. Because of this, movement of the piston 18 to the Fig. 6 position (in which passages 52 register with ports 53) vents the control chamber 51 and thus permits spring 49 to hold the plunger 45 against the projection 48. As a result, the passages 44 will be closed throughout the pumping cycle.

If discharge pressure should now rise above the desired maximum, valve plunger 64 will be forced to the right against spring 66 and control edge 65 will open communication between inlet port 56 and outlet ports 59 and 59. Fluid now flows from discharge manifold 15 through passage 57 to the passages 61 and 61' and pressure builds up in the control manifolds 54 and 54' and ports 53 and 53. Each time a piston 18 passes through the Fig. 6 position, this increased pressure is transmitted to the control chamber 51. When the pressure in the control chamber 51 becomes sufficient to overcome the bias of spring 49, the valve plunger 45 shifts to the position shown in Figs. 11-16 thereby placing passages 44 and slots 47 in registry with each other. Now, as each piston moves on its discharge stroke and passes the position in which edge 39' interrupts communication between working chamber 19 and inlet passage 26 through port 38 (see Fig. 13), communication between restricted passage 74 and passages 44 permits fluid to flow from working chamber 19 to the by-pass port 71 Since the back pressure created by the restriction in passage 74 is less than that created by check .valve 35, the check valve will not open. As the piston 18 continues to move on its discharge stroke, passages 44 are brought into registry with port 38 and for the balance of the stroke (see Figs. 15 and 16) fluid displaced by piston 18 is returned to inlet passage 26 through the ports in cap 43, bore 46, slots 47, passages 44 and port 38. The restriction to flow through this flow path is small and, therefore, check valve 35 does not open. Consequently, no fluid discharges from port 13.

It should be noted that during that portion of the discharge stroke between the Figs. 13 and 16 positions, the passages 52 leading to the control chamber 51 are closed, This arrangement is necessary in order to lock plunger 45 in the zero displacementestablishing position. It should also be noted that during this same portion of the discharge stroke, passages 44 are in communication with either restricted passage 74 or port 38. Since the flow path between working chamber 19 and by-pass port 71 offers little resistance to flow and the flow path from this working chamber to port 3 8 is practically unrestricted, the back pressure in the working chamber and the loads on the piston are small. This unloading of the pistons during zero displacement operation is a factor contributing to the high efiiciency of the If discharge pressure remains at the makirnum, the pistons 18 and 18' will continue to draw fluid from passages 26 and 26' into the working chambers 19 and 19 on their suction strokes and return most of that fluid during the discharge stroke. The small amount of fluid which is discharged through by-pass port 71 serves to cool the pump during this operation at zero efiective displacement.

When discharge pressure decreases and control valve 55 interrupts flow to passages 61 and 61, the control manifolds 54 and 54 and ports 53 and 53' are vented through restricted passage 69. Now when a piston 18 comes to the Fig; 12 position, the pressure in control chamber 51 is relieved and spring 49 shifts valve plunger 45to the left, interrupting communication between passages 44 and slots 47. After this shift occurs, all of the fluid displaced by piston 18 during that portion-of the discharge stroke between the Fig.7 position and the Fig. 10 position is dischargedffrom port 13. H I

From the preceding discussion; it will be apparent that the present displacementcontrolling mechanism has only two basic modes of operation, namely, maximum displacement operation and zero displacement operation. The full-line curve 75-7677 in Fig. 17 illustrates this characteristic. In that figure, the pressure represented by the point 76 is the discharge pressure prevailing in port 13 which causes valve 55 to establish a pressure in the control chambers 51 and 51' sufiicient to overcome the bias of springs 49 and 49' and shift the plungers 45 and 45' to the Figs. 11-16 position. Since effective displacement reduces to zero once this pressure is reached, further increases in discharge pressure cannot occur and therefore, curve portion 76--77 is a vertical line in Fig. 17.

In some cases, for example when the pump is used in a system that has a relatively high rate of leakage, it'

is more economical to reduce pump displacement in a step-like manner. The present embodiment operates in this manner when the springs 49, 49 exert unequal biases. For example, suppose that one pair of springs 49, 49 is stiffer than the others. In this case, that control chamber pressure which is produced by discharge pressure 76 and which is sufiicient to shift the six normal plungers 45 and 45 to their zero displacement-establishing position is insufiicient to shift the remaining plungers. Con: sequently, at this discharge pressure, effective displacement of vthe pump will equal the effective displacement of one pair of pistons 18, 18. If discharge pressure should now increase to that value at which even the remaining plungers are shifted to their zero displacement-establishing position (represented by point 78 in Fig. 17), pump displacement will reduce to zero. The characteristic displacement versus discharge pressure curve for this type of pump is represented by the curve 75-76-79-78- 81in Fig. 17.

The above-mentioned modification is not practical when a more gradual displacement versus discharge pressure relationship is desired because too many different springs are required. When a chaarctcn'stic curve such as the one shown in Fig. 20 is required, then the embodiment illustrated in Figs. 18 and 19 may be used. This alternate pump is exactly the same as theone shown in Figs. 1-16 except for the control manifolds. In this case, the control manifold 153 is a passage of morerestricted cross-section and it is arranged to connect the seven control ports 53 in series. The entrance end 154 of the manifold is connected by passage 61 with the out let port 59 of control valve 55 and the exit end 155 communicates with the space 14 within housing 11. With this arrangement, the manifold sections between successive connections to the control ports and between the last such connection and space 14 constitute flow restrictions and therefore there will be a pressure gradient from the entrance 154 to the exit 155. This is illustrated by Fig. 21. In this embodiment, all of the springs 49 exert the same bias so the plunger 45 associated with the control port 53 which connects at point a will be the first one to shift to the zero displacementestablishing position. As discharge pressure rises and valve 55 increases the rate of flow into passages 61 and- 61', the pressure along the control manifolds will rise and the effective displacement of the pistons will be reduced in the sequence b-c-d-e-fg.

As stated previously, the drawings and description relate only to a preferred embodiment of the invention. Since many changes can be made in the'structure of this embodiment without departing from the inventive concept, the following claims should provide the sole measure of the scope of the invention.

What is claimed is:

1. In a pump of the type including a housing containing inlet and outlet ports, a cylinder bore, a piston reciprocable in the cylinder bore and defining therewith a pump working chamber, and inlet and discharge passages leading from the working chamber to the inlet and discharge ports, respectively, the improvement which comprises a spill-backport formed in the surface of the cylinder bore and connected with the inlet port; a spill-back passage formed in the piston and leading from the working chamber through the surface of the piston, the opening through the surface of the piston beingso located that the spill-back passage and spill back port communicate at least for a portion of each discharge stroke; a control port formed in the surface of the cylinder bore; a control chamber in the piston; a control passage communicating with the control chamber and opening through the surface of the piston, the openingin the surface of the piston being so located that the control passage and port communicate at some time during each pumping cycle; a spill-back valve located within the piston and controlling flow through the spill-,.

back passage, the valve being shiftable between passage opening and passage-closing positions; a spring reacting between the piston and the spill-back valve for urgingthe valveinthe passage-closing direction; means connected with the spill-back valve and subject to the pressure in the control chamber for shifting the spill-back valve in the opposite direction against the bias of the spring; and means connected with the control port and serving to transmit to that port a variable control pressure.

2. The improvement defined in claim 1 in which the inlet passage passes through the spill-back port, and the movement of the piston controls flow from the inlet port into the working chamber.

3. The improvement defined in claim 1 in which the control port is so located that it communicates with the control passage when the piston is in a position in its stroke adjacent its bottom dead-center position but is isolated from that passage when the piston is in its bottom dead-center position.

,4. The improvement defined in claim 1 in which the control port is so located that it communicates with the control passage when the piston is in a position in its stroke. adjacent its bottom dead-center position but is isolated from that passage when the piston is in its bottorn dead-center position, and all other positions,

5. The improvement defined in claim 1 including a by-pass port formed in the housing; and a restricted bypass passage communicating with the bypass port and intersecting the cylinder bore, the intersection being so located that the spill-back passage communicates with the by-pass passage for a portion of each discharge stroke.

6. The improvement defined in claim 5 in which the spill-back passage is in communication with either the by-pass passage or the spill-back port for the entire effective discharge stroke of the piston.

7. In a pump of the type including a housing containing inlet and discharge ports, a plurality of cylinder bores, a piston reciprocable in each cylinder bore and defining therewith a working chamber, and inlet and discharge passages leading from each working chamber to the inlet and discharge ports, respectively, the improvement which comprisesa spill-back port located in the surface of each cylinder bore and connected with the inlet port; a spill-back passage formed in each piston and leading from the associated working chamber through the surface of the piston, the opening through the surface of the piston being so located that the spill-back passage and associated spill-back port communicate for at least a portion of each discharge stroke; a control port formed in the surface of each cylinder bore; a control chamber in each piston; a control passage in each piston communicating with the control chamber and opening through the surface of the piston, the opening in the surface of the piston being so located that the control passage and port communicate at some time during each pumping cycle; a spill-back valve located within each piston and controlling flow through the spill-back passage, each valve being shiftable between passageopening and passage-closing positions; a spring reacting between each piston and its spill-back valve for urging the valve in the passage-closing direction; means carried by each spill-back valve and responsive to the pressure in the associated control chamber for shifting the valve in the passage-opening direction against the bias of the spring; a control manifold interconnecting the control ports; and control means connected with the control manifold and serving to establish in it a variable control pressure. I v a 8. The improvement defined in claim 7 in which all of the springs exert the same bias.

9. The improvement defined in claim 7 in which at least one of the springs exerts a greater bias than the others.

10. The improvement defined in claim 7 in which the control means comprises a restricted vent passage leading from the control manifold; and a control valve having an inlet port connected with the pump discharge port, an outlet port connected with the control manifold, and a movable member for graduating flow from the inlet to the outlet port.

11. The improvement defined in claim 10in which the movable member is biased in the flow reducing direction by a spring and is shifted in the opposite direction by a device which is responsive to the discharge pressure of the pump.

12. The improvement defined in claim 7 in which the control manifold connects the control ports in series and contains a flow restriction between successive connections to the control ports; and in which the control means comprises a restricted vent leading from one end of the manifold, and a control valve for graduating flow into the opposite end of the manifold.

13. The improvement defined in claim 7 including a by-pass port formed in the housing; and restricted bypass passages, each communicating with the by-pas's port and one intersecting each cylinder bore, the intersections being so located that the spill-back passage communicates with the by-pass passage for a portion of each discharge stroke.

14. The improvement defined in claim 13 in which each spill-back passage communicates with either the associated by-pass passage or spill-back port for the entire effective discharge stroke of the piston.

15. In a pump of the type including a housing containing inlet and discharge ports, a cylinder bore, a piston reciprocable in the cylinder bore and defining therewith a pump Working chamber, and inlet and discharge passages leading from the working chamber to the inlet and discharge ports, respectively, the improvement which comprises a spill-back port formed in the surface of the cylinder bore; a control port formed in the surface of the cylinder bore between the spill-back port and the bottom dead-center end of the cylinder bore; an axial bore formed in the piston, the end of said bore remote from the working chamber being closed and the opposite end being in communication with that chamber; a valve plunger slidable in the axial bore and defining with the closed end thereof a control chamber, one end of the plunger being subject to the pressure in the control chamber and movable thereby in a direction to increase the volume of that chamber; a control passage connected with the control chamber and opening through the surface of the piston, the opening being so located that the control port and passage are isolated from each other when the piston is in its bottom dead-center position, are connected with each other for a short time near the beginning of the discharge stroke, and are isolated again for the balance of the discharge stroke; a first spill-back passage communicating with the axial bore and opening through the surface ofthe piston, the opening being so located that the spill-back port and passage communicate for a portion of each discharge stroke; a second spill-back passage formed in the valve plunger and communicating with the end of the axial bore opposite the control chamber, said passage terminating in an opening in the surface of the plunger which is arranged to move into and out of registry with the first spill-back passage as the valve plunger moves in control chamber volumeincreasing and volume-decreasing directions, respectively; a spring reacting between the piston and the valve plunger and urging the latter in the control chamber volumedecreasing direction; a control valve having an inlet port connected with the pump discharge port, an outlet port connected with the control port, and a movable member for graduating flow from the inlet port to the outlet port; a restricted vent passage connected wit-h the control port; and means connected with the movable member and subject to pump discharge pressure for shifting the movable member in the flow-increasing and flow-decreasing directions as discharge pressure increases and decreases, respectively.

16. The improvement defined in claim 15 in which the inlet passage passes through the spill-back port and the piston is provided with an edge for controlling flow between the working chamber and the inlet passage through the spill-backport; and including a by-pass port formed in the housing; and a by-pass passage connected with the by-pass port and intersecting the cylinder bore, the intersection being so arranged that the first spillback passage communicates with the by-pass passage for a portion of each discharge stroke. v

17. The improvement defined in claim 16 in which the parts are so arranged that each discharge stroke consists essentially of three sequential phases of operation, namely, a first phase during which the control edge is overtravelling and closing the spill-back port, a second phase during which the first spill-back passage communicates with the by-pass passage, and a third phase during which the first spill-back passage communicates with the spillback port. 7

18. The improvement defined in claim 17 in which the control passage and control port are so located that they communicate only during said first phase.

No references cited.

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